3D Image Display And 3D Image Display Method

ABSTRACT

A small, inexpensive three-dimensional image display having a structure for displaying a color three-dimensional image sharply even if a low-resolution spatial optical modulating element is used. The three-dimensional image display has an illumination light source unit, a transmission spatial optical modulating element, a lens, and a mask. The illumination light source unit includes three point light sources outputting illumination light components having wavelengths (red, green, blue) different from one another. The point light source outputting the blue illumination light component of the shortest wavelength is disposed in position B (0, 0) on the optical axis of an illumination optical system, the point light source outputting the red illumination light component is disposed in position R (x r , 0), and the point light source outputting the green illumination light component is disposed in position G (x g , 0). An aperture section of the mask is disposed in the region where the zero-order diffracted waves of the reproduction light components of the three wavelengths after subjected to wavefront conversion by the lens are superposed on one another. The illumination optical system determines the direction of incidence of each of the illumination optical components of the three wavelengths on the spatial optical modulation element.

TECHNICAL FIELD

The present invention relates to an apparatus and a method for makingillumination light components of multiple wavelengths incident to ahologram, thereby generating reproduced light components of thewavelengths from the hologram, and displaying a 3D image based on thesereproduced light components.

BACKGROUND ART

A 3D image display apparatus making use of a hologram is configured togenerate a reproduced light component from a hologram under illuminationwith an illumination light component and to display a 3D image from thereproduced light component thus generated. Another 3D image displayapparatus is configured to make illumination light components ofmultiple wavelengths (e.g., three-color components of red, green, andblue) incident to a hologram, thereby enabling color display of a 3Dimage.

A first conventional technology known heretofore is a technology ofmaking use of a photographic plate permitting high-resolution recording.In this first conventional technology, hologram recording is carried outby making reference light components and object light components ofrespective wavelengths incident to a photographic plate and therebymultiply recording holograms associated with the respective wavelengthson the photographic plate. On the other hand, reproduction isimplemented by making illumination light components of the samewavelengths as those in the recording, incident from an identicalincident direction to the holograms to generate reproduced lightcomponents of the wavelengths. This results in superimposing images ofthese reproduced light components on each other at the same position,thereby obtaining a color 3D image.

However, since in this first conventional technology the hologramsassociated with the respective wavelengths are multiply recorded on thephotographic plate, the illumination light component of a wavelengthλ_(a) is incident to the hologram associated with the wavelength λ_(a)to generate the reproduced light component of the wavelength λ_(a), andthe illumination light component of another wavelength λ_(b)(λ_(a)·λ_(b)) is also incident to the hologram associated with thewavelength λ_(a) to generate a reproduced light component of thewavelength λ_(b) from the hologram associated with the wavelength λ_(a)as well. Among these reproduced light component of wavelength λ_(a) andreproduced light component of wavelength λ_(b), the reproduced lightcomponent of wavelength λ_(a) is the light component necessary for colordisplay of the original 3D image. In contrast to it, the reproducedlight component of wavelength λ_(b) is a light component reproduced at adifferent position and at a different magnification from those of theoriginal 3D image, and is thus a crosstalk component against theoriginal 3D image to hider display of the 3D image. In order to avoidsuch crosstalk, therefore, recording is carried out by making thereference light components of multiple wavelengths incident frommutually different directions to the photographic plate where the objectlight components are incident approximately normally to the photographicplate, whereby crosstalk light components are prevented from beingsuperimposed on the original 3D image in the reproduction.

As a second conventional technology, Kunihiko Takano et al. “Study ofcolor holography 3D television with white light,” Proceedings of 3DImage Conference 2000, pp179-182 discloses a technology of making use ofthree types of spatial light modulators capable of presenting ahologram. Specifically, a first spatial light modulator presents ahologram associated with red light, a second spatial light modulator ahologram associated with green light, and a third spatial lightmodulator a hologram associated with blue light. Then a red illuminationlight component is made incident to the first spatial light modulator, agreen illumination light component to the second spatial lightmodulator, and a blue illumination light component to the third spatiallight modulator, whereby reproduced light components generated from therespective spatial light modulators are spatially superimposed, andzero-order transmitted light is removed by a mask disposed in asubsequent stage, thereby obtaining a color 3D image.

Furthermore, a third conventional technology is the technology describedin Japanese Patent Application Laid-Open No. 2000-250387, whichpositively makes use of the pixel structure of the spatial lightmodulator being discrete. Specifically, when parallel light is madeincident into an ordinary diffraction grating, there appear not only azero-order diffracted wave but also first and higher-order diffractedwaves. Likewise, reproduced light components generated from a spatiallight modulator having the discrete pixel structure also include azero-order diffracted wave and higher-order diffracted waves. Concerningtwo adjacent pixels in a spatial light modulator, where a presentationrange is limited to a range in which phase differences between syntheticwavefronts of an object light component and a reference light componentare less than n (i.e., a range without alias components) and where ahologram is presented on the spatial light modulator, wavefronts ofhigher-order diffracted waves of reproduced light components generatedfrom the spatial light modulator upon incidence of the illuminationlight component coincide with those of the zero-order diffracted waves.However, directions of emergence from the spatial light modulator aredifferent among orders. The reproduced light components undergowavefront transformation to be separated at intervals of λf/P in eachorder of the diffracted waves on the rear focal plane of a lens providedbehind the spatial light modulator. Here λ is the wavelength of theillumination light component, f the focal length of the lens, and P thepixel pitch of the spatial light modulator. Therefore, a desired 3Dimage is obtained in a manner of disposing a mask with an aperture ofrectangular shape having the length of λ/P on each side on the rearfocal plane of the lens and letting the zero-order diffracted wave ofthe reproduced light components pass through this aperture. Thehigher-order diffracted waves are blocked by this mask on the otherhand.

In the above third conventional technology, concerning two adjacentpixels in the spatial light modulator, where the presentation range islimited to a range in which phase differences between syntheticwavefronts of an object light component and a reference light componentare not less than π and are less than 2π (i.e., a range including afirst-order alias component) and where a hologram is presented on thespatial light modulator, the wavefronts of the higher-order diffractedwaves of the reproduced light components generated from the spatiallight modulator upon incidence of the illumination light componentcoincide with the zero-order diffracted wave. For this reason, thezero-order diffracted wave and all the higher-order diffracted wavesinclude their first-order alias component. Only a desired first-orderdiffracted wave among the reproduced light components can be extractedin a manner of disposing a mask with an aperture of rectangular shapehaving the length of λf/P on each side on the rear focal plane of thelens disposed behind the spatial light modulator and letting thefirst-order diffracted wave of the reproduced light components passthrough this aperture. The zero-order diffracted wave and the second andhigher-order diffracted waves are blocked by the mask on the other hand.

Namely, the above third conventional technology is to present thehologram on the spatial light modulator while limiting the presentationrange to the range including the alias component of a specific order andto extract the diffracted wave of the specific order out of thereproduced light components by use of the mask with the aperture at theposition corresponding to the specific order. The presentation of thehologram and the selection of the aperture associated with each orderare implemented based on time-sharing or spatial synthesis, therebyenabling expansion of the emergence direction range of the reproducedimage (i.e., a viewing area) formed by the lens.

DISCLOSURE OF THE INVENTION

Inventors studied each of the aforementioned first to third conventionaltechnologies and found the following problems. Namely, the firstconventional technology is suitable for cases making use of thephotographic plate capable of high-resolution recording. With use of aspatial light modulator having a low spatial resolution, however, itdoes not allow setting of a large angle of incidence of the illuminationlight component to the spatial light modulator, so that the reproducedlight components serving as crosstalk upon reproduction are superimposedon the original 3D image. As discussed in the description of the thirdconventional technology, there occurs superposition of diffracted wavesof respective orders generated from the spatial light modulator havingthe discrete pixel structure. In this respect, it is difficult to applythe foregoing first conventional technology to the spatial lightmodulator having the discrete pixel structure and low resolution.

The second conventional technology involves the spatial superposition ofreproduced light components generated from the respective spatial lightmodulators, but requires a half mirror for the superposition. For thisreason, the second conventional technology brings about an increase inthe scale of apparatus and a reduction in the light quantity of thereproduced light components. In order to compensate for the reduction inthe light quantity of the reproduced light components, the secondconventional technology requires laser light sources for outputtinglaser light of high power as the illumination light components, or adielectric mirror having wavelength selectivity, which makes theapparatus itself expensive.

The third conventional technology is directed toward the objective ofexpansion of the viewing area and the illumination light component of asingle wavelength is made incident normally to the spatial lightmodulator. Therefore, this third conventional technology is neither atechnology of making illumination light components of multiplewavelengths incident to a spatial light modulator, nor a technology ofmaking an illumination light component obliquely incident to the spatiallight modulator. The third conventional technology has a problem ofincrease in the scale of the apparatus itself due to the spatialsynthesis and a problem of increase in the cost of the apparatus itselfdue to the necessity for provision of a high-speed shutter on the rearfocal plane of the lens for time-sharing.

The present invention has been accomplished in order to solve theproblems as described above, and an object of the invention is toprovide a compact and inexpensive 3D image display apparatus and a 3Dimage display method capable of presenting color display of a clear 3Dimage even with use of a spatial light modulator of a low resolution.

A 3D image display apparatus according to the present invention is anapparatus for making illumination light components of multiplewavelengths incident to a hologram, thereby generating reproduced lightcomponents of the wavelengths from the hologram, and displaying a 3Dimage based on these reproduced light components. Specifically, the 3Dimage display apparatus according to the present invention comprises aspatial light modulator, an illumination optical system, a reproducedimage transforming optical system, and a mask. The spatial lightmodulator has a discrete pixel structure to present holograms associatedwith the respective wavelengths. The illumination optical systemconverts each of the illumination light components of the wavelengthsinto a parallel plane wave, and makes the parallel plane waves incidentfrom mutually different incident directions to the spatial lightmodulator. The reproduced image transforming optical system subjectseach of reproduced images of the wavelengths generated from theholograms presented on the spatial light modulator, to wavefronttransformation into a virtual image or a real image. The mask has anaperture provided on a focal plane of the reproduced image transformingoptical system. Particularly, in the 3D image display apparatusaccording to the present invention, the illumination optical system setsthe incident directions of the respective illumination light componentsof the wavelengths to the spatial light modulator so that diffractedwaves of any order out of the reproduced light components of thewavelengths are superimposed on each other in the aperture after thewavefront transformation by the reproduced image transforming opticalsystem.

A 3D image display method according to the present invention is a methodof making illumination light components of multiple wavelengths incidentto a hologram, thereby generating reproduced light components of thewavelengths from the hologram, and displaying a 3D image based on thesereproduced light components. Specifically, the method comprisespreparing a spatial light modulator having a discrete pixel structurefor presenting holograms associated with the respective wavelengths,letting an illumination optical system convert each of the illuminationlight components of the wavelengths into a parallel plane wave and makethe parallel plane waves incident from mutually different incidentdirections to the spatial light modulator, letting a reproduced imagetransforming optical system subject each of reproduced images of thewavelengths generated from the holograms presented on the spatial lightmodulator, to wavefront transformation into a virtual image or a realimage, placing a mask with an aperture on a focal plane of thereproduced image transforming optical system, and letting theillumination optical system set the incident directions of therespective illumination light components of the wavelengths to thespatial light modulator so that diffracted waves of any order out of thereproduced light components of the wavelengths are superimposed on eachother in the aperture after the wavefront transformation by thereproduced image transforming optical system.

According to the present invention, the holograms associated with therespective wavelengths are presented on the spatial light modulatorhaving the discrete pixel structure. The illumination optical systemconverts each of the illumination light components of the wavelengthsinto a parallel plane wave and makes the parallel plane waves incidentfrom the mutually different incident directions to this spatial lightmodulator. Each of the reproduced images of the wavelengths generatedfrom the holograms presented on the spatial light modulator is subjectedto the wavefront transformation by the reproduced image transformingoptical system into a virtual image or a real image. The mask with theaperture is disposed on the focal plane of the reproduced imagetransforming optical system. Then the incident directions of therespective illumination light components of the wavelengths to thespatial light modulator are set by the illumination optical system sothat the diffracted waves of any order out of the reproduced lightcomponents of the wavelengths are superimposed on each other in theaperture after the wavefront transformation by the reproduced imagetransforming optical system.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, the illumination optical systempreferably comprises a plurality of monochromatic light sources havingtheir respective output wavelengths different from each other, aplurality of pinholes disposed in proximity to the respectivemonochromatic light sources, and a collimating optical system forcollimating light having been emitted from the respective monochromaticlight sources and having passed through the pinholes.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, the illumination optical systempreferably comprises an achromatic lens having an identical focal lengthfor the light components of the wavelengths, and the reproduced imagetransforming optical system preferably comprises an achromatic lenshaving an identical focal length for the light components of thewavelengths.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, more preferably, the incidentdirections of the respective illumination light components of thewavelengths to the spatial light modulator are set by the illuminationoptical system so that zero-order diffracted waves of the respectivereproduced light components of the wavelengths are superimposed on eachother in the aperture after the wavefront transformation by thereproduced image transforming optical system.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, the incident directions of therespective illumination light components of the wavelengths to thespatial light modulator may be so set by the illumination optical systemthat an illumination light component of any one specific wavelength outof the wavelengths is normally incident to the spatial light modulatorand that a zero-order diffracted wave of a reproduced light component ofthe specific wavelength and a higher-order diffracted wave of areproduced light component of another wavelength are superimposed oneach other in the aperture after the wavefront transformation by thereproduced image transforming optical system.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, where P represents a pixel pitch ofthe spatial light modulator, f a focal length of the reproduced imagetransforming optical system, n₁ an order of a diffracted wave of areproduced light component of a shortest wavelength λ₁ out of thewavelengths, and n_(i) an order of a diffracted wave of a reproducedlight component of another wavelength λ_(i), an incidence angle θ_(I),of an illumination light component of the wavelength λ_(i) to thespatial light modulator is expressed by an equation below:θ_(i)=sin⁻¹ {(n ₁λ₁ −n _(i)λ_(i))/P}, andthe aperture is preferably of a rectangular shape having a length of notmore than λ₁f/P on each side.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, preferably, the spatial lightmodulator has a transmission type structure in which the reproducedlight components are emitted on the side opposite to the side where theillumination light components are incident, or a reflection typestructure in which the reproduced light components are emitted on thesame side as the side where the illumination light components areincident. In a case where the spatial light modulator has the reflectiontype structure, the illumination optical system and the reproduced imagetransforming optical system preferably share one or more opticalcomponents.

In the 3D image display apparatus or the 3D image display methodaccording to the present invention, the spatial light modulator may beprovided with microlenses for respective pixels.

Each of embodiments of the present invention will become more fullyunderstandable in view of the detailed description and accompanyingdrawings which will follow. It is noted that these embodiments arepresented merely for illustrative purposes only but are not to beconstrued in a way of limiting the invention.

The range of further application of the present invention will becomeapparent in view of the following detailed description. However, thedetailed description and specific examples will describe the preferredembodiments of the present invention, but it is apparent that they arepresented for illustrative purposes only and that various modificationsand improvements falling within the spirit and scope of the presentinvention are obvious to those skilled in the art in view of thedetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a configuration of a first embodimentof the 3D image display apparatus according to the present invention;

FIG. 2 is an illustration for explaining an illumination optical systemand a spatial light modulator of the 3D image display apparatusaccording to the first embodiment;

FIG. 3 is an illustration for explaining the illumination optical systemof the 3D image display apparatus according to the first embodiment;

FIG. 4 is an illustration for explaining a display operation of aluminescent point in a 3D image in a case where a blue illuminationlight component is normally incident to the spatial light modulator, inthe 3D image display apparatus according to the first embodiment;

FIG. 5 is an illustration for explaining a hologram presented on thespatial light modulator when the blue illumination light component isnormally incident to the spatial light modulator, in the 3D imagedisplay apparatus according to the first embodiment;

FIG. 6 is an illustration for explaining a display operation of aluminescent point in a 3D image in a case where an illumination lightcomponent is obliquely incident to the spatial light modulator, in the3D image display apparatus according to the first embodiment;

FIG. 7 and FIG. 8 are illustrations for explaining holograms prepared bya first hologram preparing method;

FIG. 9 is an illustration for explaining a display operation of aluminescent point in a 3D image in a case where an illumination lightcomponent is obliquely incident to the spatial light modulator while thehologram shown in FIG. 7 is presented on the spatial light modulator;

FIG. 10 is an illustration for explaining a second hologram preparingmethod;

FIG. 11 is an illustration showing arrangement of point light sources ofthree wavelengths in an ideal case;

FIG. 12 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a red reproduced light component at themask position, in the ideal case;

FIG. 13 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a green reproduced light component at themask position, in the ideal case;

FIG. 14 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a blue reproduced light component at themask position, in the ideal case;

FIG. 15 is an illustration showing the wavefront transformation areas ofzero-order diffracted waves of respective reproduced light components ofred, green, and blue at the mask position, in the ideal case;

FIG. 16 is an illustration showing arrangement of three point lightsources in an illumination light source section 10 of the 3D imagedisplay apparatus according to the first embodiment;

FIG. 17 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a red reproduced light component at themask location in the 3D image display apparatus according to the firstembodiment;

FIG. 18 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a green reproduced light component at themask location in the 3D image display apparatus according to the firstembodiment;

FIG. 19 is an illustration showing wavefront transformation areas ofzero-order diffracted waves of respective reproduced light components ofred, green, and blue at the mask location in the 3D image displayapparatus according to the first embodiment;

FIG. 20 is an illustration showing arrangement of three point lightsources in an illumination light source section in modification exampleA of the 3D image display apparatus according to the first embodiment;

FIG. 21 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a red reproduced light component at themask location, in modification example A of the 3D image displayapparatus according to the first embodiment;

FIG. 22 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a green reproduced light component at themask location, in modification example A of the 3D image displayapparatus according to the first embodiment;

FIG. 23 is an illustration showing wavefront transformation areas ofzero-order diffracted waves of respective reproduced light components ofred, green, and blue at the mask location, in modification example A ofthe 3D image display apparatus according to the first embodiment;

FIG. 24 is an illustration showing arrangement of three point lightsources in an illumination light source section in modification exampleB of the 3D image display apparatus according to the first embodiment;

FIG. 25 is an illustration showing a wavefront transformation area of azero-order diffracted wave of a green reproduced light component at themask location, in modification example B of the 3D image displayapparatus according to the first embodiment;

FIG. 26 is an illustration showing wavefront transformation areas ofzero-order diffracted waves of respective reproduced light components ofred, green, and blue at the mask location, in modification example B ofthe 3D image display apparatus according to the first embodiment;

FIG. 27 is an illustration showing a configuration of a secondembodiment of the 3D image display apparatus according to the presentinvention;

FIG. 28 is an illustration showing a configuration of a third embodimentof the 3D image display apparatus according to the present invention;

FIG. 29 is an illustration showing wavefront transformation areas ofzero-order diffracted waves of respective reproduced light components ofred, green, and blue at the mask location in the 3D image displayapparatus according to the third embodiment;

FIG. 30 is an illustration showing a configuration of a fourthembodiment of the 3D image display apparatus according to the presentinvention;

FIG. 31 and FIG. 32 are illustrations showing wavefront transformationareas of diffracted waves of each order of respective reproduced lightcomponents of red, green, and blue at the mask location in the 3D imagedisplay apparatus according to the fourth embodiment;

FIG. 33 is an illustration for explaining a spatial light modulator anda wavefront transforming optical system in the 3D image displayapparatus according to the fourth embodiment;

FIG. 34 is an illustration for explaining a relation between an angle ofincidence of an illumination light component and an angle of emergenceof a reproduced light component in the spatial light modulator of the 3Dimage display apparatus according to the fourth embodiment;

FIG. 35 is an illustration showing a configuration of a fifth embodimentof the 3D image display apparatus according to the present invention;and

FIG. 36 is an illustration showing a configuration of a sixth embodimentof the 3D image display apparatus according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Each of embodiments of the 3D image display apparatus and 3D imagedisplay method according to the present invention will be describedbelow in detail with reference to FIGS. 1-4 to FIG. 36. Identical orequivalent elements will be denoted by the same reference symbols in thedescription of the drawings, without redundant description. Forconvenience sake of description, a coordinate system in each drawing isthe xyz orthogonal coordinate system in which the z-axis is definedalong a direction normal to the spatial light modulator.

First Embodiment

First, the first embodiment of the 3D image display apparatus and 3Dimage display method according to the present invention will bedescribed. FIG. 1 is an illustration showing a configuration of thefirst embodiment of the 3D image display apparatus according to thepresent invention. The 3D image display apparatus 1 shown in this figurehas an illumination light source section 10, a lens 20, a spatial lightmodulator 30 of the transmission type, a lens 40, and a mask 50. Theillumination light source section 10 and the lens 20 constitute anillumination optical system for converting each of illumination lightcomponents of three wavelengths into a parallel plane wave and makingthe parallel plane waves incident from mutually different incidentdirections to the spatial light modulator 30. The lens 40 constitutes areproduced image transforming optical system for subjecting each ofreproduced images of the three wavelengths generated from hologramspresented on the spatial light modulator 30, to wavefront transformationinto a virtual image or a real image.

The illumination light source section 10 has three point light sourcesfor emitting their respective illumination light components of mutuallydifferent wavelengths (red, green, and blue) These three point lightsources are located at mutually different positions on a straight lineparallel to the x-axis. The point light source for emitting the blueillumination light component of the shortest wavelength is located at aposition B(0,0) on the optical axis of the illumination optical system.The point light source for emitting the red illumination light componentis located at a position R(x_(r), 0). The point light source foremitting the green illumination light component is located at a positionG(x_(g), 0). Each point light source includes, for example, a lightemitting diode, a laser diode, or the like and emits an illuminationlight component with excellent monochromaticity. The point light sourceseach are sequentially lit as pulsed in time series.

The lens 20 has the optical axis parallel to the z-axis, and collimateseach of illumination light components of the respective wavelengthsemitted from the three corresponding point light sources of theillumination light source section 20, into a parallel plane wave andmakes the parallel plane waves incident from mutually different incidentdirections to the spatial light modulator 30. In a case where the lens20 is comprised of a single convex lens, the spacing between each of thethree point light sources and the lens 20 is equal to the focal lengthof the lens 20. Since the three point light sources are located at theaforementioned positions, the blue illumination light component isnormally incident to the spatial light modulator 30, while theillumination light components of red and green are obliquely incident tothe spatial light modulator 30. The lens 20 is preferably an achromaticlens having an identical focal length for the wavelengths of therespective illumination light components.

The spatial light modulator 30 is a transmission type spatial lightmodulator having the discrete pixel structure, and sequentially presentsholograms associated with the three respective wavelengths, in timeseries. These holograms may be amplitude holograms or phase holograms.Then the spatial light modulator 30 sequentially presents hologramsassociated with wavelengths at respective points of time, in synchronismwith time-series sequential incidence of the illumination lightcomponents of the respective wavelengths from the lens 20. This resultsin sequentially outputting reproduced light components of the respectivewavelengths in time series. Namely, the field sequential system isadopted for the spatial light modulator 30.

The lens 40 functions to subject each of reproduced images of the threewavelengths generated from the holograms presented on the spatial lightmodulator 30, to wavefront transformation into a virtual image or a realimage, and then to make each image pass on the plane of the mask 50. Ina case where the lens 40 is comprised of a single convex lens, thespacing between the lens 40 and the mask 50 is equal to the focal lengthof the lens 40. The lens 40 is preferably an achromatic lens having anidentical focal length for the wavelengths of the respectiveillumination light components.

The mask 50 is provided on the focal plane of the lens 40 and has anaperture 51. This aperture 51 has a rectangular shape each side of whichis parallel to the x-axis or to the y-axis, and has a function ofselecting only diffracted waves of zero order generated from the spatiallight modulator 30, a function of blocking zero-order directlytransmitted light from the spatial light modulator 30, and a function ofblocking unwanted light of light components of zero-order diffractedwaves which are generated from the holograms presented on the spatiallight modulator 30 and which form a real image or a conjugate image tocause the problem of double images. The zero-order directly transmittedlight from the spatial light modulator 30 is light contributing to imageformation of the light sources as condensed by the lens 40, and becomesbackground light of a reproduced image to degrade contrast. The aperture51 is located in an area in which diffracted waves of any order out ofthe reproduced light components of the three wavelengths aresuperimposed on each other after the wavefront transformation by thelens 40. Particularly, in the present embodiment, the aperture 51 islocated in an area where the zero-order diffracted waves of therespective reproduced light components of the three wavelengths aresuperimposed on each other after the wavefront transformation by thelens 40. In this manner, the incident directions of the respectiveillumination light components of the three wavelengths to the spatiallight modulator 30 are set by the illumination optical system.

FIG. 2 is an illustration for explaining the illumination optical systemand spatial light modulator 30 of the 3D image display apparatus 1according to the first embodiment. As shown in this figure, the bluepoint light source in the illumination light source section 10 islocated on the optical axis of the lens 20, and the illumination lightcomponent emitted from this blue point light source is collimated by thelens 20 into a parallel plane wave 60 _(b) to be normally incident tothe spatial light modulator 30. The red point light source is located atthe position separated from the optical axis of the lens 20, and theillumination light component emitted from this red point light source iscollimated by the lens 20 into a parallel plane wave 60 _(r) travelingin a direction 61 _(r) inclined relative to the z-axis to be obliquelyincident to the spatial light modulator 30. The green point light sourceis located in a manner similar to the red point light source.

FIG. 3 is an illustration for explaining the illumination optical systemof the 3D image display apparatus 1 according to the first embodiment.As shown in this figure, the illumination light source section 10includes three monochromatic light sources 11 _(r), 11 _(g), and 11 _(b)of mutually different output wavelengths, and three pinholes 12 _(r), 12_(g), and 12 _(b). The pinhole 12 _(r) is located at the positionR(x_(r), 0) in proximity to the monochromatic light source 11 _(r) foremitting the red light, and outputs the light emitted from thismonochromatic light source 11 _(r), toward the lens 20. The pinhole 12_(g) is located at the position G(x_(g), 0) in proximity to themonochromatic light source 11 _(g) for emitting the green light, andoutputs the light emitted from this monochromatic light source 11 _(g),toward the lens 20. The pinhole 12 _(b) is located at the positionB(0,0) in proximity to the monochromatic light source 11 _(b) foremitting the blue light, and outputs the light emitted from thismonochromatic light source 11 _(b), toward the lens 20. By adopting thisconfiguration, even in a case where each of the monochromatic lightsources 11 _(r), 11 _(g), and 11 _(b) cannot be treated as a point lightsource, the illumination light component emitted from each of thepinholes 12 _(r), 12 _(g), and 12 _(b) can be treated as light emittedfrom a point light source and the lens 20 can convert it into an idealparallel plane wave.

Next, the operation of the 3D image display apparatus 1 according to thefirst embodiment will be described. In a case where an element capableof modulating both the amplitude and phase for each pixel is applied asthe spatial light modulator 30, neither transmitted light nor aconjugate image is generated. However, in a case where an elementcapable of modulating only one of the amplitude and phase for each pixelis applied as the spatial light modulator 30, transmitted light and aconjugate image are generated. The below will describe the latter case.

FIG. 4 is an illustration for explaining a display operation of aluminescent point in a 3D image where the blue illumination lightcomponent is normally incident to the spatial light modulator 30 in the3D image display apparatus 1 according to the first embodiment. FIG. 5is an illustration for explaining a hologram presented on the spatiallight modulator 30 when the blue illumination light component isnormally incident to the spatial light modulator 30 in the 3D imagedisplay apparatus 1 according to the first embodiment. When a hologram31 _(b) associated with the blue illumination light component ispresented on the spatial light modulator 30, the blue illumination lightcomponent of a parallel plane wave 60 _(b) is normally incident to thespatial light modulator 30. The hologram 31 _(b) associated with theblue illumination light component is presented on a half plane (an areaof y<0) on the spatial light modulator 30. When the illumination lightcomponent is incident to the spatial light modulator 30, a reproducedimage 62 _(b) and a conjugate image 63 _(b) of a luminescent point inthe 3D image are formed on the optical axis, and zero-order transmittedlight appears. The reproduced image 62 _(b) of the luminescent point issubjected to wavefront transformation into an area 52 _(b) (in the areaof y<0) on the mask 50 by the lens 40. On the other hand, the conjugateimage 63 _(b) of the luminescent point is subjected to wavefronttransformation into an area 53 _(b) (in the area of y>0) on the mask 50by the lens 40. The zero-order transmitted light is converged at theposition (0,0) on the mask 50 by the lens 40. Then the conjugate imageand the zero-order transmitted light are blocked by the mask 50, and thereproduced image only can be observed through the aperture 51.

FIG. 6 is an illustration for explaining a display operation of aluminescent point in a 3D image in a case where an illumination lightcomponent is obliquely incident to the spatial light modulator 30 in the3D image display apparatus 1 according to the first embodiment. Ahologram presented at this time on the spatial light modulator 30 isassumed to be similar to the hologram shown in FIG. 5. In this case, theillumination light component of a parallel plane wave 60 is obliquelyincident to the spatial light modulator 30, whereupon a reproduced image62 and a conjugate image 63 of the luminescent point in the 3D image areformed on the optical axis 61 of the parallel plane wave 60. This isdifferent from the locations of the reproduced image and conjugate imageshown in FIG. 4.

In order to avoid the disagreement between the reproduced image upon thenormal incidence and the reproduced image upon the oblique incidence,the present embodiment is arranged to prepare the holograms presentedupon the oblique incidence on the spatial light modulator 30, by eitherof two methods described below.

The first hologram preparing method is a method of calculating theholograms upon the oblique incidence. An object light component from aluminescent point forming a 3D image is expressed by a spherical wave.An object light component O_(ij) generated from a luminescent point at aposition (x₀,y₀,L₀) is expressed by Eqs (1a), (1b) below, at a position(x_(i),y_(j),0) on the spatial light modulator 30. $\begin{matrix}{O_{i,j} = {\frac{1}{r}{\exp({jkr})}}} & \left( {1a} \right) \\{r = \sqrt{\left( {x_{i} - x_{0}} \right)^{2} + \left( {y_{j} - y_{0}} \right)^{2} + L_{0}^{2}}} & \left( {1b} \right)\end{matrix}$

Here r represents a distance from the luminescent point at the position(x₀,y₀,L₀) to the position (x_(i),y_(j),0) on the spatial lightmodulator 30, and k the wave number of the object light component. Areference light component R_(ij) being a parallel plane wave with anincidence angle θ is expressed by Eq (2) below, at the position(x_(i),y_(j),0) on the spatial light modulator 30.R _(i,j)=exp(jk(L ₀−(x _(i) −x _(θ))sin θ))  (2)

When the synthesis of the object light component and the reference lightcomponent on the hologram plane is expressed by Eq (3) below, the phaseφ_(i,j) of light is expressed by Eq (4) below and the light intensity byEq (5) below, at the position (x_(i),y_(j),0) on the hologram plane.O _(i,j) +R _(i,j) =A+jB  (3)φ_(i,j)=tan⁻¹(B/A)  (4)|O _(i,j) +R _(i,j)|² =|O _(i,j)|² +|R _(i,j)|hu 2 +O _(i,j) R _(i,j)*+O _(i,j) *R _(i,j)  (5)

Since the illumination light component incident to the spatial lightmodulator 30 upon reproduction is equivalent to the reference lightcomponent R, a computer-generated hologram is prepared from the thirdterm in the right-hand side of above Eq (5).

Concerning the calculation range of the computer-generated hologram, themaximum spatial frequency of the hologram is restricted by the pixelpitch of the spatial light modulator 30, because the spatial lightmodulator 30 displaying the hologram has the discrete pixel structure.For this reason, the calculation range is a range in which phasedifferences between synthetic wavefronts of the object light componentand the reference light component at two adjacent pixels are not morethan π, i.e., a half plane determined by a region satisfying theconditions expressed by Expressions (6a), (6b) below.|φ_(i,j)−φ_(i−1,j)|≦π  (6a)|φ_(i,j)−φ_(i,j−1)|≦π  (6b)

FIGS. 7 and 8 are illustrations each for explaining a hologram preparedby the first hologram preparing method. FIG. 7 shows a presentationrange of hologram 31 on the spatial light modulator 30 in a case where apoint light source is located at the position (0,y). FIG. 8 shows apresentation range of hologram 31 on the spatial light modulator 30 in acase where a point light source is located at the position (x,0). Asshown in these figures, the hologram 31 presented on the spatial lightmodulator 30 is similar to one obtained by translating the hologram 31_(b) shown in FIG. 5, in parallel with the x-axis or with the y-axis.

FIG. 9 is an illustration for explaining a display operation of aluminescent point in a 3D image where an illumination light component isobliquely incident to the spatial light modulator 30 during presentationof the hologram 31 shown in FIG. 7, on the spatial light modulator 30.As shown in this figure, when the illumination light component of aparallel plane wave 60 is obliquely incident to the spatial lightmodulator 30, a reproduced image 62 of the luminescent point in the 3Dimage is formed on the optical axis 61. This coincides with the locationof the reproduced image shown in FIG. 4.

The second hologram preparing method is a method of translating ahologram presentation range. The foregoing first hologram preparingmethod requires the process of calculating the product of the objectlight component and the reference light component in calculation of thehologram because of the oblique incidence of the reference lightcomponent, so that the computation time is longer than in the case ofthe normal incidence of the reference light component. In contrast toit, the second hologram preparing method described below is able tocalculate the hologram within a short time by making use of thesimilarity of the hologram upon the oblique incidence to that upon thenormal incidence as described above.

FIG. 10 is an illustration for explaining the second hologram preparingmethod. Supposing the hologram presented on the spatial light modulator30 is the same as the hologram shown in FIG. 5, a location ofluminescent point 62′ generated therefrom is a distance D apart in thex-axis direction from a location of desired luminescent point 62.Therefore, the hologram to be presented can be obtained by translatingthe presentation location of the hologram by this distance D. Thistranslation distance D is expressed by Eq (7) below.D=L·tan θ  (7)

Here L represents the distance between the luminescent point and thehologram plane. Furthermore, θ is an incidence angle of the parallelplane wave to the hologram plane, and this incidence angle θ isexpressed by Eq (8) below.θ=(distance between light source and optical axis)/(front focal lengthof lens 20)  (8)

The first or second hologram preparing method described above enablesthe reproduced images to be acquired without deviation between upon theoblique incidence and upon the normal incidence.

Next, reproduced light components generated from the spatial lightmodulator 30 upon incidence of the illumination light components of therespective wavelengths will be described.

FIGS. 11 to 15 are illustrations for explaining an ideal case presentedas a comparative example. It is assumed that the spatial light modulator30 herein is an element capable of modulating only one of the amplitudeand phase for each pixel and that a hologram is presented on the halfplane (y<0) of the spatial light modulator 30 as shown in FIG. 5, andthe case described herein is assumed to be an ideal case where all thepoint light sources of the three wavelengths are located at the position(0,0) as shown in FIG. 11.

In this case, as shown in FIG. 12, the zero-order diffracted wave of thered reproduced light component of the longest wavelength generated fromthe spatial light modulator 30 is subjected to wavefront transformationby the lens 40 into a rectangular area 52 _(r) defined by four points R1to R4 expressed by Expressions (9) below, on the rear focal plane of thelens 40.R 1(−λ_(r) f/2P _(x), 0)R 2(−λ_(r) f/2P _(x) , −λ _(r) f/2P_(y))R 3(+λ_(r) f/2P _(x) , −λ _(r) f/2P_(y))R 4(+λ_(r) f/2P _(x), 0)  (9)

Here λ_(r) is the wavelength of the red reproduced light component, fthe focal length of the lens 40, P_(x) the pixel pitch in the x-axisdirection of the spatial light modulator 30, and P_(y) the pixel pitchin the y-axis direction of the spatial light modulator 30. A redconjugate image is subjected to wavefront transformation into arectangular region defined by four points R1 and R4-R6 expressed byExpressions (10) below, on the rear focal plane of the lens 40.R 1(−λ_(r) f/2P_(x), 0)R 4(+λ_(r) f/2P _(x), 0)R 5(+λ_(r) f/2P _(x) , +λ _(r) f/2P _(y))R 6(−λ_(r) f/2P _(x) , +λ _(r) f/2P _(y))  (10)

With the rectangular region defined by four points R2, R3, R5, and R6,as a unit, zero-order and higher-order reproduced images and conjugateimages are two-dimensionally periodically formed on the rear focal planeof the lens 40.

Likewise, as shown in FIG. 13, the zero-order diffracted wave of thegreen reproduced light component of the wavelength λ_(g) generated fromthe spatial light modulator 30 is subjected to wavefront transformationby the lens 40 into a rectangular area 529 defined by four points G1-G4expressed by Expressions (11) below, on the rear focal plane of lens 40.G 1(−λ_(g) f/2P _(x), 0)G 2(−λ_(g) f/2P _(x) , −λ _(g) f/2P _(y))G 3(+λ_(g) f/2P _(x) , −λ _(g) f/2P _(y))G 4(+λ_(g) f/2P _(x), 0)  (11)

In addition, as shown in FIG. 14, the zero-order diffracted wave of theblue reproduced light component of the shortest wavelength λ_(b)generated from the spatial light modulator 30 is subjected to wavefronttransformation by the lens 40 into a rectangular area 52 _(b) defined byfour points B1-B4 expressed by Expressions (12) below, on the rear focalplane of the lens 40.B 1(−λ_(b) f/2P _(x), 0)B 2(−λ_(b) f/2P _(x) , −λ _(b) f/2P _(y))B 3(+λ_(b) f/2P _(x) , −λ _(b) f/2P _(y))B 4(+λ_(b) f/2P _(x), 0)  (12)

When the wavefront transformation areas 52 _(r), 52 _(g), and 52 _(b) onthe rear focal plane of the lens 40 are shown in a superimposed state asshown in FIG. 15, the green wavefront transformation area52 _(g) isincluded in the red wavefront transformation area 52 _(r), and the bluewavefront transformation area 52 _(b) is included in the green wavefronttransformation area 52 _(g), Therefore, a full-color 3D image can beobserved when the aperture 51 of the mask 50 is set to be equivalent tothe blue wavefront transformation area 52 _(b) and when the reproducedlight components of the respective colors having passed through thisaperture 52 are observed.

However, the ideal case where the three point light sources are locatedat the common position as shown in FIG. 11 is practically impossible. Inthe present embodiment, therefore, the three point light sources arelocated at mutually different positions, an illumination light componentof one wavelength out of them is made normally incident to the spatiallight modulator 30, and the other illumination light components ofremaining two wavelengths are made obliquely incident to the spatiallight modulator 30.

FIGS. 16 to 19 are illustrations to illustrate the 3D image displayapparatus 1 and 3D image display method according to the firstembodiment. FIG. 16 is an illustration showing arrangement of the threepoint light sources in the illumination light source section 10 of the3D image display apparatus 1 according to the first embodiment. FIG. 17is an illustration showing a wavefront transformation area of thezero-order diffracted wave of the red reproduced light component at thelocation of mask 50 in the 3D image display apparatus 1 according to thefirst embodiment. FIG. 18 is an illustration showing a wavefronttransformation area of the zero-order diffracted wave of the greenreproduced light component at the location of mask 50 in the 3D imagedisplay apparatus 1 according to the first embodiment. The wavefronttransformation area of the zero-order diffracted wave of the bluereproduced light component at the location of mask 50 in the 3D imagedisplay apparatus 1 according to the first embodiments is the same asthat in the case shown in FIG. 14. FIG. 19 is an illustration showingthe wavefront transformation areas of the zero-order diffracted waves ofthe respective reproduced light components of red, green, and blue atthe location of mask 50 in the 3D image display apparatus 1 according tothe first embodiment.

In the first embodiment, as shown in FIG. 16, the red point light sourceis located at the position R(x_(r),0), the green point light source atthe position G(x_(g),0), and the blue point light source at the positionB(0,0). Here x_(r) and x_(g) each are expressed by Expressions (13)below.x _(r)=+{(λ_(g) f/2P)−(λ_(b) f/2P)}/Mx _(g)=−{(λ_(g) f/2P)−(λ_(b) f/2P)}/MM=−f ₂ /f ₂  (13)

Here f₁ represents the focal length of lens 20, and f₂ the focal lengthof the lens 40. M is a magnification of the optical system.

In this case, as shown in FIG. 17, the zero-order diffracted wave of thered reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into a rectangular area 52 _(r) based on a positionR′(λ_(g)f/2P−λ_(b)f/2P,0), on the rear focal plane of lens 40. As shownin FIG. 18, the zero-order diffracted wave of the green reproduced lightcomponent generated from the spatial light modulator 30 is subjected towavefront transformation by the lens 40 into a rectangular area 52 _(g)based on a position G′(−λ_(g)f/2P+λ_(b)f/2P,0), on the rear focal planeof lens 40. As shown in FIG. 14, the zero-order diffracted wave of theblue reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into a rectangular area 52 _(b) based on the position B′(0,0), on therear focal plane of lens 40.

When the wavefront transformation areas 52 _(r), 52 _(g), and 52 _(b) onthe rear focal plane of lens 40 are shown in a superimposed state asshown in FIG. 19, the green wavefront transformation area 529 isincluded in the red wavefront transformation area 52 _(r), and the bluewavefront transformation area 52 _(b) is included in the green wavefronttransformation area 52 _(g). Therefore, a full-color 3D image can beobserved when the aperture 51 of the mask 50 is made coincident with theblue wavefront transformation area 52 _(b) and when the reproduced lightcomponents of the respective colors having passed through the aperture52 are observed.

Next, a specific example of the first embodiment will be described. Thespatial light modulator 30 used herein was a data projection liquidcrystal panel LCX023AL (pixel pitch P=26 μm) available from Sony Corp.The lens 20 was an achromatic lens having the focal length of 600 mm,and the lens 40 an achromatic lens having the focal length of 150 mm.The monochromatic light source 11 _(r) for emitting red light was alight emitting diode CL-280SR-C (wavelength 650 nm; dimensions 1.0(L)×0.5 (W)×0.6 (H)) available from Citizen Electronics Co., Ltd. Themonochromatic light source 11 _(g) for emitting green light was a lightemitting diode E1S07-AG1A7-02 (wavelength 530 nm; dimensions 1.6 (L)×0.6(W)×1.15 (H)) available from TOYODA GOSEI Co., Ltd. The monochromaticlight source 11 _(b) for emitting blue light was a light emitting diodeE1S07-AB1A7-02 (wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H))available from TOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (−0.69 mm, 0) and the monochromatic light source 11 _(g)for emitting green light at the position (+0.69 mm, 0). The aperturediameter of each of the pinholes 12 _(r), 12 _(g), and 12 _(b) was 150μm. The incidence angle of the red illumination light component to thespatial light modulator 30 was set at +0.07°, and the incidence angle ofthe green illumination light component to the spatial light modulator 30at −0.07°. The size of the aperture 51 of the mask 50 was 2.7 mm (W)×1.3mm (H). The drive frequency of the spatial light modulator 30 was 70 Hz,the holograms associated with the respective colors (wavelengths) weresequentially presented on the spatial light modulator 30, and the threemonochromatic light sources 11 _(r), 11 _(g), and 11 _(b) weresequentially activated in synchronism therewith, whereby a full-color 3Dimage was clearly observed through the aperture 51 of the mask 50.

Next, modification example A of the 3D image display apparatus and 3Dimage display method according to the first embodiment will bedescribed. The description heretofore concerned the arrangement of thethree point light sources along the x-axis direction, whereas thismodification example A concerns arrangement of the three point lightsources along the y-axis direction. FIGS. 20 to 23 are illustrations forexplaining modification example A of the 3D image display apparatus 1and 3D image display method according to the first embodiment. FIG. 20is an illustration showing arrangement of the three point light sourcesin the illumination light source section 10 in modification example A ofthe 3D image display apparatus 1 according to the first embodiment. FIG.21 is an illustration showing the wavefront transformation area of thezero-order diffracted wave of the red reproduced light component at thelocation of mask 50, in modification example A of the 3D image displayapparatus 1 according to the first embodiment. FIG. 22 is anillustration showing the wavefront transformation area of the zero-orderdiffracted wave of the green reproduced light component at the locationof mask 50, in modification example A of the 3D image display apparatus1 according to the first embodiment. In modification example A of the 3Dimage display apparatus 1 according to the first embodiment, thewavefront transformation area of the zero-order diffracted wave of theblue reproduced light component at the location of mask 50 is the sameas that in the case shown in FIG. 14. FIG. 23 is an illustration showingthe wavefront transformation areas of the zero-order diffracted waves ofthe respective reproduced light components of red, green, and blue atthe location of mask 50, in modification example A of the 3D imagedisplay apparatus 1 according to the first embodiment.

In this modification example A, as shown in FIG. 20, the red point lightsource is located at the position R(0,y_(r)), the green point lightsource at the position G(0,y_(g)), and the blue point light source atthe position B(0,0). Here y_(r) and y_(g) each are expressed by Eqs (14)below.y _(r)={(λ_(r) f/2P)−(λ_(b) f/2P)}/My _(g)={(λ_(g) f/2P)−(λ_(b) f/2P)}/M

In this case, as shown in FIG. 21, the zero-order diffracted wave of thered reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into a rectangular area 52 _(r) based on a positionR′(0,λ_(r)f/2P−λ_(b)f/2P,0), on the rear focal plane of lens 40. Inaddition, as shown in FIG. 22, the zero-order diffracted wave of thegreen reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into a rectangular area 52 _(g) based on a positionG′(0,λ_(g)f/2P−λ_(b)f/2P,0), on the rear focal plane of lens 40.Furthermore, as shown in FIG. 14, the zero-order diffracted wave of theblue reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into the rectangular area 52 _(b) based on the position B′(0,0), on therear focal plane of lens 40.

When the wavefront transformation areas 52 _(r), 52 _(g), and 52 _(b) onthe rear focal plane of lens 40 are shown in a superimposed state asshown in FIG. 23, the green wavefront transformation area 52 _(g) isincluded in the red wavefront transformation area 52 _(r), and the bluewavefront transformation area 52 _(b) is included in the green wavefronttransformation area 52 _(g). Therefore, a full-color 3D image can beobserved when the aperture 51 of the mask 50 is made coincident with theblue wavefront transformation area 52 _(b) and when the reproduced lightcomponents of the respective colors having passed through this aperture52 are observed.

Next, a specific example of modification example A of the firstembodiment will be described. The spatial light modulator 30 used hereinwas a data projection liquid crystal panel LCX023AL (pixel pitch P=26μm) available from Sony Corp. The lens 20 was an achromatic lens havingthe focal length of 600 mm, and the lens 40 an achromatic lens havingthe focal length of 150 mm. The monochromatic light source 11 _(r) foremitting red light was a light emitting diode CL-280SR-C (wavelength 650nm; dimensions 1.0 (L)×0.5 (W)×0.6 (H)) available from CitizenElectronics Co., Ltd. The monochromatic light source 11 _(g) foremitting green light was a light emitting diode E1S07-AG1A7-02(wavelength 530 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd. The monochromatic light source 11 _(b) foremitting blue light was a light emitting diode E1S07-AB1A7-02(wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (0, −2.08 mm) and the monochromatic light source 11 _(g)for emitting green light at the position (0, −0.69 mm). The aperturediameter of each of the pinholes 12 _(r), 12 _(g), and 12 _(b) was 150μm. The incidence angle of the red illumination light component to thespatial light modulator 30 was set at −0.20°, and the incidence angle ofthe green illumination light component to the spatial light modulator 30at −0.07°. The size of the aperture 51 of the mask 50 was 2.7 mm (W)×1.3mm (H). The drive frequency of the spatial light modulator 30 was 70 Hz,the holograms associated with the respective colors (wavelengths) weresequentially presented on the spatial light modulator 30, and the threemonochromatic light sources 11 _(r), 11 _(g), and 11 _(b) weresequentially activated in synchronism therewith, whereby a full-color 3Dimage was clearly observed through the aperture 51 of the mask 50.

Next, modification example B of the 3D image display apparatus and 3Dimage display method according to the first embodiment will bedescribed. In the foregoing modification example A the three point lightsources were arranged in the y-axis direction on the half plane (y<0),whereas in this modification example B the red point light source isplaced on one half plane (y<0) and the green point light source on theother half plane (y>0). FIGS. 24 to 26 are illustrations for explainingmodification example B of the 3D image display apparatus 1 and 3D imagedisplay method according to the first embodiment. FIG. 24 is anillustration showing arrangement of the three point light sources in theillumination light source section 10, in modification example B of the3D image display apparatus 1 according to the first embodiment. FIG. 25is an illustration showing the wavefront transformation area of thezero-order diffracted wave of the green reproduced light component atthe location of mask 50, in modification example B of the 3D imagedisplay apparatus 1 according to the first embodiment. In modificationexample B of the 3D image display apparatus 1 according to the firstembodiment, the wavefront transformation area of the zero-orderdiffracted wave of the red reproduced light component at the location ofmask 50 is the same as that in the case shown in FIG. 21. Inmodification example B of the 3D image display apparatus 1 according tothe first embodiment, the wavefront transformation area of thezero-order diffracted wave of the blue reproduced light component at thelocation of mask 50 is the same as that in the case shown in FIG. 14.FIG. 26 is an illustration showing the wavefront transformation areas ofthe zero-order diffracted waves of the respective reproduced lightcomponents of red, green, and blue at the location of mask 50, inmodification example B of the 3D image display apparatus 1 according tothe first embodiment.

In this modification example B, as shown in FIG. 24, the red point lightsource is located at the position R(0,y_(r)), the green point lightsource at the position G(0,y_(g)), and the blue point light source atthe position B(0,0). Here y_(r) and y_(g) each are expressed by Eqs (15)below.y _(t){(λ_(r) f/2P)−(λ_(b) f/2P)}/My _(g)=−(λ_(b) f/2P)/M  (15)

In this case, as shown in FIG. 21, the zero-order diffracted wave of thered reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into a lower rectangular area 52 _(r) based on the positionR′(0,λ_(r)f/2P−λ_(b)f/2P,0), on the rear focal plane of lens 40. Inaddition, as shown in FIG. 25, the zero-order diffracted wave of thegreen reproduced light component generated from the spatial lightmodulator 30 is subjected to wavefront transformation by the lens 40into an upper rectangular area 52 _(g) based on the positionG′(0,−λ_(b)f/2P,0), on the rear focal plane of lens 40. Furthermore, asshown in FIG. 14, the zero-order diffracted wave of the blue reproducedlight component generated from the spatial light modulator 30 issubjected to wavefront transformation by the lens 40 into the lowerrectangular area 52 _(b) based on the position B′(0,0), on the rearfocal plane of lens 40.

When the wavefront transformation areas 52 _(r), 52 _(g), and 52 _(b) onthe rear focal plane of lens 40 are shown in a superimposed state asshown in FIG. 26, the green wavefront transformation area 52 _(g) isincluded in the red wavefront transformation area 52 _(r), and the bluewavefront transformation area 52 _(b) is included in the green wavefronttransformation area 52 _(g). Therefore, a full-color 3D image can beobserved when the aperture 51 of the mask 50 is made coincident with theblue wavefront transformation area 52 _(b) and when the reproduced lightcomponents of the respective colors having passed through this aperture52 are observed.

Next, a specific example of modification example B of the firstembodiment will be described. The spatial light modulator 30 used hereinwas a data projection liquid crystal panel LCX023AL (pixel pitch P=26μm) available from Sony Corp. The lens 20 was an achromatic lens havingthe focal length of 200 mm, and the lens 40 an achromatic lens havingthe focal length of 150 mm. The monochromatic light source 11 _(r) foremitting red light was a light emitting diode CL-280SR-C (wavelength 650nm; dimensions 1.0 (L)×0.5 (W)×0.6 (H)) available from CitizenElectronics Co., Ltd. The monochromatic light source 11 _(g) foremitting green light was a light emitting diode E1S07-AG1A7-02(wavelength 530 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd. The monochromatic light source 11 _(b) foremitting blue light was a light emitting diode E1S07-AB1A7-02(wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (0, −0.69 mm) and the monochromatic light source 11 _(g)for emitting green light at the position (0, +1.36 mm). The aperturediameter of each of the pinholes 12 _(r), 12 _(g), and 12 _(b) was 150μm. The incidence angle of the red illumination light component to thespatial light modulator 30 was set at −0.20°, and the incidence angle ofthe green illumination light component to the spatial light modulator 30at +0.39°. The size of the aperture 51 of the mask 50 was 2.7 mm (W)×1.3mm (H). The drive frequency of the spatial light modulator 30 was 70 Hz,the holograms associated with the respective colors (wavelengths) weresequentially presented on the spatial light modulator 30, and the threemonochromatic light sources 11 _(r), 11 _(g), and 11 _(b) weresequentially activated in synchronism therewith, whereby a full-color 3Dimage was clearly observed through the aperture 51 of the mask 50.

As described above, the 3D image display apparatus 1 and 3D imagedisplay method according to the first embodiment, including modificationexample A and modification example B, are able to provide color displayof a clear 3D image even with use of the spatial light modulator 30 of alow resolution, because the incident directions of the respectiveillumination light components of the three wavelengths to the spatiallight modulator 30 are properly set and the zero-order diffracted wavesof the respective reproduced light components of the three wavelengthsgenerated from the spatial light modulator 30 are superimposed on eachother in the aperture 51 after the wavefront transformation by the lens40. There is no need for the half mirror for superposition of thereproduced light components of the three wavelengths as required inconventional technology 2, and no need for the high-speed shutter asrequired in the third conventional technology, and thus the presentembodiment successfully provides the compact and inexpensive 3D imagedisplay apparatus.

Second Embodiment

Next, the second embodiment of the 3D image display apparatus and 3Dimage display method according to the present invention will bedescribed. FIG. 27 is an illustration showing a configuration of the 3Dimage display apparatus 2 according to the second embodiment. The 3Dimage display apparatus 2 shown in this figure has an illumination lightsource section 10, a lens 20, a half mirror 25, a reflection typespatial light modulator 30, a lens 40, and a mask 50. The illuminationlight source section 10, lens 20, and half mirror 25 constitute anillumination optical system for converting each of illumination lightcomponents of three wavelengths into a parallel plane wave and makingthe parallel plane waves incident from mutually different incidentdirections to the spatial light modulator 30. The half mirror 25 andlens 40 constitute a reproduced image transforming optical system forsubjecting each of reproduced light components of the three wavelengthsgenerated from holograms presented on the spatial light modulator 30, towavefront transformation. The illumination optical system and thereproduced image transforming optical system share the half mirror 25.

When compared with the first embodiment, the 3D image display apparatus2 and 3D image display method according to the second embodiment aresimilar thereto in each of the illumination light source section 10,lens 20, lens 40, and mask 50, but are different therefrom in mutualarrangement of the components due to the spatial light modulator 30being the reflection type spatial light modulator. When compared withthe first embodiment, the operation of the 3D image display apparatus 2,and the 3D image display method according to the second embodiment aredifferent therefrom in that each illumination light component, afterconverted into a parallel plane wave by the lens 20, passes through thehalf mirror 25 to enter the spatial light modulator 30, in that thereproduced light components emerge on the same side as the side wherethe illumination light components are incident to the spatial lightmodulator 30, and in that each reproduced light component is subjectedto wavefront transformation by the lens 40 after reflected by the halfmirror 25. For the rest, the operation of the 3D image display apparatus2, and the 3D image display method according to the second embodimentare theoretically similar to those in the first embodiment (includingmodification examples A and B).

Next, a specific example of the second embodiment will be described. Thespatial light modulator 30 used herein was a reflection type liquidcrystal panel MD800G6 for micro monitor (pixel pitch P=12.55 μm)available from Micro Display Corp. The lens 20 was an achromatic lenshaving the focal length of 300 mm, and the lens 40 an achromatic lenshaving the focal length of 60 mm. The monochromatic light source 11 _(r)for emitting red light was a light emitting diode CL-280SR-C (wavelength650 nm; dimensions 1.0 (L)×0.5 (W)×0.6 (H)) available from CitizenElectronics Co., Ltd. The monochromatic light source 11 _(g) foremitting green light was a light emitting diode E1S07-AG1A7-02(wavelength 530 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd. The monochromatic light source 11 _(b) foremitting blue light was a light emitting diode E1S07-AB1A7-02(wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (−0.72 mm, 0) and the monochromatic light source 11 _(g)for emitting green light at the position (+0.72 mm, 0). The aperturediameter of each of the pinholes 12 _(r), 12 _(g), and 12 _(b) was 150μm. The incidence angle of the red illumination light component to thespatial light modulator 30 was set at −0.14°, and the incidence angle ofthe green illumination light component to the spatial light modulator 30at +0.14°. The size of the aperture 51 of the mask 50 was 2.2 mm (W)×1.1mm (H). The drive frequency of the spatial light modulator 30 was 90 Hz,the holograms associated with the respective colors (wavelengths) weresequentially presented on the spatial light modulator 30, and the threemonochromatic light sources 11 _(r), 11 _(g), and 11 _(b) weresequentially activated in synchronism therewith, whereby a full-color 3Dimage was clearly observed through the aperture 51 of the mask 50.

Third Embodiment

Next, the third embodiment of the 3D image display apparatus and 3Dimage display method according to the present invention will bedescribed. FIG. 28 is an illustration showing a configuration of the 3Dimage display apparatus 3 according to the third embodiment. The 3Dimage display apparatus 3 shown in this figure has an illumination lightsource section 10, a half mirror 25, a lens 20, a reflection typespatial light modulator 30, and a mask 50. The illumination light sourcesection 10, half mirror 25, and lens 20 constitute an illuminationoptical system for converting each of illumination light components ofthree wavelengths into a parallel plane wave and making the parallelplane waves incident from mutually different incident directions to thespatial light modulator 30. The lens 20 and half mirror 25 constitute areproduced image transforming optical system for subjecting each ofreproduced light components of the three wavelengths generated fromholograms presented on the spatial light modulator 30, to wavefronttransformation. The illumination optical system and the reproduced imagetransforming optical system share the lens 20 and the half mirror 25.

When compared with the second embodiment, the 3D image display apparatus3 and 3D image display method according to the third embodiment aresimilar thereto in each of the illumination light source section 10,spatial light modulator 30, and mask 50, but are different therefrom inmutual arrangement of the components because of the spatial lightmodulator 30 being the reflection type spatial light modulator. Whencompared with the case of the second embodiment, the operation of the 3Dimage display apparatus 3, and the 3D image display method according tothe third embodiment are different therefrom in that the lens 20 alsoacts as the lens 40, in that each illumination light component, afterpassing through the half mirror 25, is converted into a parallel planewave by the lens 20 to enter the spatial light modulator 30, in that thereproduced light components emerge on the same side as the side wherethe illumination light components are incident to the spatial lightmodulator 30, and in that each reproduced light component is subjectedto wavefront transformation as reflected by the half mirror 25 afterpassing through the lens 20. For the rest, the operation of the 3D imagedisplay apparatus 2, and the 3D image display method according to thethird embodiment are theoretically almost similar to those in the secondembodiment.

Since in the third embodiment the lens 20 also acts as the lens 40, thefocal lengths of the illumination optical system and the reproducedimage transforming optical system are equal to each other. Therefore,where the three point light sources are located at positions R(x_(r),0),G(x_(g),0), and B(0,0), reference points of the wavefront transformationareas of the respective colors on the plane of mask 50 are positionsR(−x_(r),0), G(−x_(g), 0) and B(0,0). The area where all the wavefronttransformation areas 52 _(r), 52 _(g), and 52 _(b) of the respectivecolors on the plane of mask 50 are superimposed on each other (i.e., thearea of the aperture 51 of the mask 50) can be narrower than in the caseof the first embodiment or the second embodiment, as shown in FIG. 29.

Next, a specific example of the third embodiment will be described. Thespatial light modulator 30 used herein was a reflection type liquidcrystal panel MD800G6 for micro monitor (pixel pitch P=12.55 μm)available from Micro Display Corp. The lens 20 also acting as the lens40 was an achromatic lens having the focal length of 60 mm. Themonochromatic light source 11 _(r) for emitting red light was a lightemitting diode CL-280SR-C (wavelength 650 nm; dimensions 1.0 (L)×0.5(W)×0.6 (H)) available from Citizen Electronics Co., Ltd. Themonochromatic light source 11 _(g) for emitting green light was a lightemitting diode E1S07-AG1A7-02 (wavelength 530 nm; dimensions 1.6 (L)×0.6(W)×1.15 (H)) available from TOYODA GOSEI Co., Ltd. The monochromaticlight source 11 _(b) for emitting blue light was a light emitting diodeE1S07-AB1A7-02 (wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H))available from TOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (−0.65 mm, 0) and the monochromatic light source 11 _(g)for emitting green light at the position (+0.65 mm, 0). The aperturediameter of each of the pinholes 12 _(r), 12 _(g), and 12 _(b) was 150μm. The incidence angle of the red illumination light component to thespatial light modulator 30 was set at −0.62°, and the incidence angle ofthe green illumination light component to the spatial light modulator 30at +0.62°. The size of the aperture 51 of the mask 50 was 1.5 mm (W)×1.1mm (H). The drive frequency of the spatial light modulator 30 was 90 Hz,the holograms associated with the respective colors (wavelengths) weresequentially presented on the spatial light modulator 30, and the threemonochromatic light sources 11 _(r), 11 _(g), and 11 _(b) weresequentially activated in synchronism therewith, whereby a full-color 3Dimage was clearly observed through the aperture 51 of the mask 50.

Fourth Embodiment

Next, the fourth embodiment of the 3D image display apparatus and 3Dimage display method according to the present invention will bedescribed. FIG. 30 is an illustration showing a configuration of the 3Dimage display apparatus 4 according to the fourth embodiment. The 3Dimage display apparatus 4 shown in this figure has an illumination lightsource section 10, a lens 20, a spatial light modulator 30 of thetransmission type, a lens 40, and a mask 50. The illumination lightsource section 10 and the lens 20 constitute an illumination opticalsystem for converting each of illumination light components of threewavelengths into a parallel plane wave and making the parallel planewaves incident from mutually different incident directions to thespatial light modulator 30. The lens 40 constitutes a reproduced imagetransforming optical system for subjecting each of reproduced images ofthe three wavelengths generated from holograms presented on the spatiallight modulator 30, to wavefront transformation into a virtual image ora real image.

The illumination light source section 10 has three point light sourcesfor emitting their respective illumination light components of mutuallydifferent wavelengths (red, green, and blue). These three point lightsources are located at mutually different positions on a straight lineparallel to the x-axis. The point light source for emitting the blueillumination light component of the shortest wavelength is located atthe position B(0,0) on the optical axis of the illumination opticalsystem. The point light source for emitting the red illumination lightcomponent is located at the position R(x_(r,)0) or R(0, y_(r)). Thepoint light source for emitting the green illumination light componentis located at the position G(x_(g),0). Each point light source includes,for example, a light emitting diode, a laser diode, or the like andemits an illumination light component with excellent monochromaticity.The point light sources each are sequentially lit as pulsed in timeseries. The configuration of this illumination light source section 10is preferably the same as that in FIG. 3.

The lens 20 has the optical axis parallel to the z-axis, and itcollimates each of the illumination light components of the respectivewavelengths emitted from the three corresponding point light sources ofthe illumination light source section 20, into a parallel plane wave andmakes the parallel plane waves incident from mutually different incidentdirections to the spatial light modulator 30. In a case where the lens20 is comprised of a single convex lens, the spacing between each of thethree point light sources and the lens 20 is equal to the focal lengthof the lens 20. Since the three point light sources are located at theaforementioned positions, the blue illumination light component isnormally incident to the spatial light modulator 30, while theillumination light components of red and green are obliquely incident tothe spatial light modulator 30. The lens 20 is preferably an achromaticlens having an identical focal length for the wavelengths of therespective illumination light components.

The spatial light modulator 30 is a transmission type spatial lightmodulator having the discrete pixel structure, and sequentially presentsholograms associated with the three respective wavelengths, in timeseries. These holograms may be amplitude holograms or phase holograms.Then the spatial light modulator 30 sequentially presents hologramsassociated with wavelengths at respective points of time, in synchronismwith time-series sequential incidence of the illumination lightcomponents of the respective wavelengths from the lens 20. This resultsin sequentially outputting reproduced light components of the respectivewavelengths in time series. Namely, the field sequential system isadopted for the spatial light modulator 30.

The lens 40 subjects each of the reproduced light components of thethree wavelengths generated from the holograms presented on the spatiallight modulator 30, to wavefront transformation onto the plane of mask50. In a case where the lens 40 is comprised of a single convex lens,the spacing between the lens 40 and the mask 50 is equal to the focallength of the lens 40. The lens 40 is preferably an achromatic lenshaving an identical focal length for the wavelengths of the respectiveillumination light components.

The mask 50 is provided on the focal plane of the lens 40 and has anaperture 51. This aperture 51 has a rectangular shape each side of whichis parallel to the x-axis or to the y-axis, and has a function ofselecting only diffracted waves of a specific order generated from thespatial light modulator 30, a function of blocking nth-order directlytransmitted light from the spatial light modulator 30, and a function ofblocking unwanted light of components of nth-order diffracted waveswhich are generated from the holograms presented on the spatial lightmodulator 30 and which form a real image or a conjugate image to causethe problem of double images. The nth-order directly transmitted lightfrom the spatial light modulator 30 is light contributing to imageformation of the light sources as condensed by the lens 40, and becomesbackground light of a reproduced image to degrade contrast. The aperture51 is located in an area in which diffracted waves of any order out ofthe reproduced light components of the three wavelengths aresuperimposed on each other after the wavefront transformation by thelens 40. Particularly, in the present embodiment, the aperture 51 isprovided in the area where the zero-order diffracted wave of the bluereproduced light component of the shortest wavelength and higher-orderdiffracted waves of the reproduced light components of the other twowavelengths are superimposed on each other after subjected to wavefronttransformation by the lens 40. In this manner, the incident directionsof the respective illumination light components of the three wavelengthsto the spatial light modulator 30 are set by the illumination opticalsystem.

The zero-order transmitted light having passed through the spatial lightmodulator 30 among the illumination light component emitted from theblue point light source at the location B(0,0) in the illumination lightsource section 10 is converged at the position B′(0,0) on the plane ofmask 50 by the lens 40. The zero-order transmitted light having passedthrough the spatial light modulator 30 among the illumination lightcomponent emitted from the red point light source at the positionR(x_(r),0) or R(0,y_(r)) in the illumination light source section 10 isconverged at the position R′(x_(r)′,0) or R′(0,y_(r)′) on the plane ofmask 50 by the lens 40. The zero-order transmitted light having passedthrough the spatial light modulator 30 among the illumination lightcomponent emitted from the blue point light source at the positionG(x_(g),0) in the illumination light source section 10 is converged atthe position G′(x_(g)′,0) on the plane of mask 50 by the lens 40.

However, since the spatial light modulator 30 has the discrete pixelstructure, as shown in FIG. 31 or FIG. 32, the image formation of theblue point light source on the plane of mask 50 obtains the wavefronttransformation of the zero-order diffracted wave at the position G₁, thewavefront transformation of the first-order diffracted wave at each ofeight positions G₂ a distance (λ_(b)f/P) apart in the direction of thex-axis or the y-axis from the position G₁, and the wavefronttransformation of higher-order diffracted waves at positions thedistance (λ_(b)f/P) each further apart in the direction of the x-axis orthe y-axis. The same also applies to the image formation of the pointlight sources of red and green. This will be detailed with reference toFIG. 33.

FIG. 33 is an illustration for explaining the spatial light modulator 30and the reproduced image transforming optical system of the 3D imagedisplay apparatus 4 according to the fourth embodiment. Let P be thepixel pitch of the spatial light modulator 30, λ_(b) be the wavelengthof the blue illumination light component normally incident to thespatial light modulator 30, n_(b) be the order of the blue diffractedwave emerging from the spatial light modulator 30, and θ₀ be theemergence angle of the n_(b)th diffracted wave of blue from the spatiallight modulator 30.

In this case, a relation given by Eq (16) below holds among theseparameters.P sin θ_(o) =n _(b)λ_(b)  (16)

From this Eq (16), the emergence angle θ_(o) of the blue n_(b)th-orderdiffracted wave from the spatial is light modulator 30 is expressed byEq (17) below.θ_(o)=sin⁻¹(n _(b)λ_(b) /P)  (17)

The blue n_(b)th-order diffracted wave from the spatial light modulator30 is converged at the position the distance A_(n) apart from theoptical axis, on the rear focal plane of lens 40 (the plane of mask 50).This distance A_(n) is represented by Eq (18) below. $\begin{matrix}\begin{matrix}{A_{n} = {f_{2}\tan\quad\theta_{\theta}}} \\{= {f_{2}\tan\left\{ {\sin^{- 1}\left( {n_{b}{\lambda_{b}/P}} \right)} \right\}}} \\{= {f_{2}t\quad\sin{\left\{ {\sin^{- 1}\left( {n_{b}{\lambda_{b}/P}} \right)} \right\}/\cos}\left\{ {\sin^{- 1}\left( {n_{b}{\lambda_{b}/P}} \right)} \right\}}} \\{= {\left( {f_{2}n_{b}{\lambda_{b}/P}} \right)\cos\left\{ {\sin^{- 1}\left( {n_{b}{\lambda_{b}/P}} \right)} \right\}}}\end{matrix} & (18)\end{matrix}$

As far as the order n_(b) is small, this Eq (18) is approximated by Eq(19) below.A _(n) =f ₂ n _(b)λ_(b))/P  (19)

As seen from these Eq (18) or Eq (19), points of convergence of thezero-order and higher-order diffracted waves appear at almost equalintervals on the rear focal plane of lens 40 (plane of mask 50), and theappearance intervals of the convergence points of diffracted waves ofrespective orders are different depending upon the wavelength. Supposingthe point light sources of the respective wavelengths in theillumination light source section 10 are present at the same position,the convergence points of the zero-order diffracted waves of thereproduced light components of the respective wavelengths appear at thesame position, but the convergence points of the higher-order diffractedwaves of the reproduced light components of the respective wavelengthsappear at different positions, on the rear focal plane of lens 40 (planeof mask 50).

The diffracted waves forming a 3D reproduced image can be extracted byusing the mask 50 with the aperture 51 based on the position expressedby above Eq (18) or Eq (19) and letting only diffracted waves of anyorder out of the reproduced light components pass through the aperture51. In a case where the spatial light modulator 30 is able to modulateboth the amplitude and phase, the diffracted waves forming the 3Dreproduced image can be extracted by placing the aperture 51 ofrectangular shape having the length of f₂λ_(b)/P on one side with thecenter at the position expressed by above Eq (18) or Eq (19). In a casewhere the spatial light modulator 30 is able to modulate only one of theamplitude and phase, the diffracted waves forming the 3D reproducedimage can be extracted by placing the aperture 51 of rectangular shapehaving the length of f₂λ_(b)/P on one side and the length of f₂λ_(b)/2Pon the other side, on the half plane based on the position expressed byabove Eq (18) or Eq (19) (a region corresponding to the hologrampresentation area on the spatial light modulator 30).

In the present embodiment, concerning the aperture 51 of the mask 50,its area is not controlled in time division for each wavelength, but isconstant independent of the wavelengths. Then the mask 51 placed hereinis one having the location and shape adapted to λ_(b) being the shortestwavelength out of the three wavelengths (λ_(r), λ_(g), λ_(b)). As forthe other two wavelengths (λ_(r), λ_(g)), the incident directions of theillumination light components to the spatial light modulator 30 are setso that their diffracted waves of any order out of the reproduced lightcomponents pass through the aperture 51. Where the spatial lightmodulator 30 is able to modulate only one of the amplitude and phase,the convergence points of reproduced waves of the orders used information of the 3D image out of the reproduced light components of therespective wavelengths are made coincident with each other, wherebythese convergence points are blocked by the mask 50. The lenses 20, 40suitably applicable herein are lenses adequately compensated forchromatic aberration and having an identical focal length for each ofthe three wavelengths (λ_(r), λ_(g), λ_(b)).

The blue illumination light component is normally incident to thespatial light modulator 30, while the other illumination lightcomponents of red and green each are obliquely incident thereto. Theconvergence point of the zero-order diffracted wave upon the normalincidence of the blue illumination light component must coincide withthe convergence points of the higher-order diffracted waves of thespecific order upon the oblique incidence of the other colorillumination light components on the rear focal plane of lens 40. Anglesof incidence of the illumination light components satisfying thiscondition will be described below with reference to FIG. 34.

FIG. 34 is an illustration for explaining the relation between the angleof incidence of an illumination light component and the angle ofemergence of a reproduced light component in the spatial light modulator30 of the 3D image display apparatus 4 according to the fourthembodiment. It is assumed that a parallel plane wave of any onewavelength λ_(i) (=λ_(r) or λ_(g)) other than the shortest wavelengthλ_(b) is incident at an incidence angle θ_(i) to the spatial lightmodulator 30 and that the diffracted wave of order n_(i) among thereproduced light component of the wavelength λ_(i) is emergent at adiffraction angle θ_(o) (the same as the blue diffracted wave is) fromthe spatial light modulator 30. The pixel pitch of the spatial lightmodulator 30 is assumed to be P.

In this case, a relation given by Eq (20) below holds among theseparameters.P sin θ_(o) −P sin θ_(i) =n _(i)λ_(i)  (20)

Rewriting this into an equation for the incidence angle θ_(i), it isexpressed by Eq (21) below.θ_(i)=sin⁻¹{(P sin θ_(o) −n _(i)λ_(i))/P}  (21)

By substituting aforementioned Eq (17), this Eq (21) is expressed by Eq(22) below.θ_(i)=sin⁻¹{(n _(b)λ_(b) −n _(i)λ_(i))/P}  (22)

When the blue illumination light component of wavelength λ_(b) isnormally incident to the spatial light modulator 30 and when theillumination light component of the wavelength λ_(i) (=λ_(r) or λ_(g))is obliquely incident at the incidence angle θ_(i) represented by aboveEq (22), to the spatial light modulator 30, the diffracted waves of anyorder among the reproduced light components of the respectivewavelengths are emergent at the same diffraction angle θ_(o) from thespatial light modulator 30 to be converged at the same point by the lens40.

From above Eq (20), the incidence angle θ_(i) and the emergence angleθ_(o) are equal to each other only when the diffraction order n_(i) isthe zero order. The zero-order diffracted wave is converged at theposition the distance A_(ni) expressed by Eq (23) below, apart from theoptical axis on the rear focal plane of lens 40. $\begin{matrix}\begin{matrix}{A_{ni} = {f_{2}\tan\quad\theta_{i}}} \\{= {f_{2}{\tan\left\lbrack {\sin^{- 1}\left\{ {\left( {{n_{b}\lambda_{b}} - {n_{i}\lambda_{i}}} \right)/P} \right\}} \right\rbrack}}} \\{= {f_{2}{\tan\left\lbrack {\sin^{- 1}\left\{ {n_{b}{\lambda_{b}/P}} \right\}} \right\rbrack}}} \\{= {{{f_{2}\left( {n_{b}{\lambda_{b}/P}} \right)}/\cos^{- 1}}\left\{ {\sin\left( {n_{b}{\lambda_{b}/P}} \right)} \right\}}}\end{matrix} & (23)\end{matrix}$

As a first example about the distance A_(ni), let us suppose that theorder n_(b) of the diffracted wave of the blue wavelength λ_(b) is 0 andthat the order n_(i) of the diffracted wave of the other wavelengthλ_(i) is −1. In this case, the incidence angle θ_(i) of the illuminationlight component of the wavelength λ_(i) is represented by Eq (24) below.θ_(i)=sin⁻¹(λ_(i) /P)  (24)

The zero-order diffracted wave of the wavelength λ_(i) is converged atthe position the distance A⁻¹ represented by Eq (25) below, apart fromthe optical axis on the rear focal plane of lens 40. $\begin{matrix}\begin{matrix}{A_{- 1} = {f_{2}\tan\quad\theta_{i}}} \\{= {f_{2}{\tan\left\lbrack {\sin^{- 1}\left( {\lambda_{i}/P} \right)} \right\rbrack}}} \\{\cong {f_{2}{\lambda_{i}/P}}}\end{matrix} & (25)\end{matrix}$

As a second example about the distance A_(ni), let us suppose that theorder n_(b) of the diffracted wave of the blue wavelength λ_(b) is 0 andthat the order n_(i) of the diffracted wave of the other wavelengthλ_(i) is +1. In this case, the incidence angle θ_(i) of the illuminationlight component of the wavelength λ_(i) is expressed by Eq (26) below.θ_(i)=sin⁻¹(−λ_(i) /P)  (26)

The zero-order diffracted wave of the wavelength λ_(i) is converged atthe position the distance A₊₁ represented by Eq (27) below, apart fromthe optical axis on the rear focal plane of lens 40. $\begin{matrix}\begin{matrix}{A_{- 1} = {f_{2}\tan\quad\theta_{i}}} \\{= {f_{2}{\tan\left\lbrack {\sin^{- 1}\left( {{- \lambda_{i}}/P} \right)} \right\rbrack}}} \\{\cong {{- f_{2}}{\lambda_{i}/P}}}\end{matrix} & (27)\end{matrix}$

The illumination light component of the wavelength λ_(i) can be madeincident as a parallel plane wave at the incidence angle θ_(i) to thespatial light modulator 30 by placing the point light source at theposition the distance B_(ni) represented by Eq (28) below, apart fromthe optical axis on the front focal plane of the lens 20 having thefocal length f₁. $\begin{matrix}\begin{matrix}{B_{ni} = {{- f_{1}}\tan\quad\theta_{i}}} \\{= {{- f_{1}}{\tan\left\lbrack {\sin^{- 1}\left\{ {\left( {{n_{b}\lambda_{b}} - {n_{1}\lambda_{1}}} \right)/P} \right\}} \right\rbrack}}}\end{matrix} & (28)\end{matrix}$

As a first example about the distance B_(ni), let us suppose that theorder n_(b) of the diffracted wave of the blue wavelength λ_(b) is 0 andthat the order n_(i) of the diffracted wave of the other wavelengthλ_(i) is −1. In this case, the point light source of the wavelengthλ_(i) is placed at the position the distance B⁻¹ represented by Eq (29)below, apart from the optical axis on the front focal plane of lens 20.$\begin{matrix}\begin{matrix}{B_{- 1} = {{- f_{1}}\tan\quad\theta_{i}}} \\{= {{- f_{1}}{\tan\left\lbrack {\sin^{- 1}\left( {\lambda_{i}/P} \right)} \right\rbrack}}} \\{\cong {{- f_{1}}{\lambda_{i}/P}}} \\{= {A_{- 1}/M}}\end{matrix} & (29)\end{matrix}$

Here M is the magnification of the optical system expressed by Eq (13).

As a second example about the distance B_(1i), let us suppose that theorder n_(b) of the diffracted wave of the blue wavelength λ_(b) is 0 andthat the order n_(i) of the diffracted wave of the other wavelengthλ_(i) is +1. In this case, the point light source of the wavelengthλ_(i) is placed at the position the distance B₊₁ represented by Eq (30)below, apart from the optical axis on the front focal plane of lens 20.$\begin{matrix}\begin{matrix}{B_{+ 1} = {{- f_{1}}\tan\quad\theta_{i}}} \\{= {{- f_{1}}{\tan\left\lbrack {\sin^{- 1}\left( {{- \lambda_{i}}/P} \right)} \right\rbrack}}} \\{\cong {f_{1}{\lambda_{i}/P}}} \\{= {{- A_{- 1}}/M}}\end{matrix} & (30)\end{matrix}$

FIG. 31 is an example in which on the front focal plane of lens 20 thered point light source is placed at the position (−f₁λ_(r)/P,0), thegreen point light source at the position (+f₁λ_(g)/P,0), and the bluepoint light source at the position (0,0) and in which on the rear focalplane of lens 40 the −1st-order diffracted wave among the red reproducedlight component, the +1st-order diffracted wave among the greenreproduced light component, and the zero-order diffracted wave among theblue reproduced light component are converged at their respectiveconvergence points coincident on the optical axis. FIG. 32 is an examplein which on the front focal plane of lens 20 the red point light sourceis placed at the position (0, −f₁λ_(r)/P), the green point light sourceat the position (+f₁λ_(g)/P,0), and the blue point light source at theposition (0,0) and in which on the rear focal plane of lens 40 the−1st-order diffracted wave among the red reproduced light component, the+1st-order diffracted wave among the green reproduced light component,and the zero-order diffracted wave among the blue reproduced lightcomponent are converged at their respective convergence pointscoincident on the optical axis.

The holograms associated with the respective colors, presented on thespatial light modulator 30, are holograms upon normal incidence of theillumination light components of the respective colors to the spatiallight modulator 30 and thus there is no need for concern about theincidence angles as described in the first embodiment, thus enablingsimple and fast computation.

Next, a specific example of the fourth embodiment will be described. Thespatial light modulator 30 used herein was a data projection liquidcrystal panel LCX023AL (pixel pitch P=26 μm) available from Sony Corp.The lens 20 was an achromatic lens having the focal length of 150 mm,and the lens 40 an achromatic lens having the focal length of 150 mm.The monochromatic light source 11 _(r) for emitting red light was alight emitting diode CL-280SR-C (wavelength 650 nm; dimensions 1.0(L)×0.5 (W)×0.6 (H)) available from Citizen Electronics Co., Ltd. Themonochromatic light source 11 _(g) for emitting green light was a lightemitting diode E1S07-AG1A7-02 (wavelength 530 nm; dimensions 1.6 (L)×0.6(W)×1.15 (H)) available from TOYODA GOSEI Co., Ltd. The monochromaticlight source 11 _(b) for emitting blue light was a light emitting diodeE1S07-AB1A7-02 (wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H))available from TOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (−3.75 mm, 0) or at the position (0, −3.75 mm) and themonochromatic light source 11 _(g) for emitting green light at theposition (+3.06 mm, 0). The aperture diameter of each of the pinholes 12_(r), 12 _(g), and 12 _(b) was 150 μm. The incidence angle of the redillumination light component to the spatial light modulator 30 was setat +1.43°, and the incidence angle of the green illumination lightcomponent to the spatial light modulator 30 at −1.17°. The size of theaperture 51 of the mask 50 was 2.7 mm (W)×1.3 mm (H). The drivefrequency of the spatial light modulator 30 was 70 Hz, the hologramsassociated with the respective colors (wavelengths) were sequentiallypresented on the spatial light modulator 30, and the three monochromaticlight sources 11 _(r), 11 _(g), and 11 _(b) were sequentially activatedin synchronism therewith, whereby a full-color 3D image was clearlyobserved through the aperture 51 of the mask 50.

In the case where the zero-order diffracted wave of the blue reproducedlight component is observed while the higher-order diffracted waves ofthe other color reproduced light components are observed, as in thepresent embodiment, the quantity of light of the higher-order diffractedwaves is smaller than that of the zero-order diffracted wave. In orderto increase the aperture efficiency, it is thus preferable to use as thespatial light modulator 30 a liquid crystal panel with macro lensesmounted for respective pixels. This results in diverging light passingthrough each pixel and increasing the light quantity of the higher-orderdiffracted waves. A liquid crystal panel LCX023CMT (pixel pitch P=26 μm)available from Sony Corp. can be used as the liquid crystal panel ofthis type. The color balance of color 3D images was improved by usingthis liquid crystal panel and adjusting the magnitude of drive currentssupplied to the respective monochromatic light sources 11 _(r), 11 _(g),and 11 _(b).

As described above, the 3D image display apparatus 4 and 3D imagedisplay method according to the fourth embodiment are able to providecolor display of a clear 3D image even with use of the spatial lightmodulator 30 of a low resolution, because the incident directions areappropriately set for the respective illumination light components ofthe three wavelengths incident to the spatial light modulator 30 and thezero-order diffracted wave or higher-order diffracted waves of thereproduced light components of the three wavelengths generated from thespatial light modulator 30 are superimposed on each other in theaperture 51 after the wavefront transformation by the lens 40. Inaddition, there is no need for the half mirror for superimposing thereproduced light components of the three wavelengths as required in thesecond conventional technology, nor for the high-speed shutter asrequired in the third conventional technology, and thus the presentembodiment successfully provides the compact and inexpensive 3D imagedisplay apparatus.

Fifth Embodiment

Next, the fifth embodiment of the 3D image display apparatus and 3Dimage display method according to the present invention will bedescribed. FIG. 35 is an illustration showing a configuration of the 3Dimage display apparatus 5 according to the fifth embodiment. The 3Dimage display apparatus 5 shown in this figure has an illumination lightsource section 10, a lens 20, a half mirror 25, a reflection typespatial light modulator 30, a lens 40, and a mask 50. The illuminationlight source section 10, lens 20, and half mirror 25 constitute anillumination optical system for converting each of illumination lightcomponents of three wavelengths into a parallel plane wave and makingthe parallel plane waves incident from mutually different incidentdirections to the spatial light modulator 30. The half mirror 25 and thelens 40 constitute a reproduced image transforming optical system forsubjecting each of reproduced light components of the three wavelengthsgenerated from holograms presented on the spatial light modulator 30, towavefront transformation into a virtual image or a real image. Theillumination optical system and the reproduced image transformingoptical system share the half mirror 25.

When compared with the fourth embodiment, the 3D image display apparatus5 and 3D image display method according to the fifth embodiment aresimilar thereto in each of the illumination light source section 10,lens 20, lens 40, and mask 50, but are different therefrom in mutualarrangement of the components due to the spatial light modulator 30being the reflection type spatial light modulator. When compared withthe fourth embodiment, the operation of the 3D image display apparatus5, and the 3D image display method according to the fifth embodiment aredifferent therefrom in that each illumination light component, afterconverted into a parallel plane wave by the lens 20, passes through thehalf mirror 25 to enter the spatial light modulator 30, in that thereproduced light components emerge on the same side as the side wherethe illumination light components are incident to the spatial lightmodulator 30, and in that each reproduced light component is subjectedto the wavefront transformation by the lens 40 after reflected by thehalf mirror 25. For the rest, the operation of the 3D image displayapparatus 5, and the 3D image display method according to the fifthembodiment are theoretically similar to those in the fourth embodiment.

Next, a specific example of the fifth embodiment will be described. Thespatial light modulator 30 used herein was a reflection type liquidcrystal panel MD800G6 for micro monitor (pixel pitch P=12.55 μm)available from Micro Display Corp. The lens 20 was an achromatic lenshaving the focal length of 120 mm, and the lens 40 an achromatic lenshaving the focal length of 60 mm. The monochromatic light source 11 _(r)for emitting red light was a light emitting diode CL-280SR-C (wavelength650 nm; dimensions 1.0 (L)×0.5 (W)×0.6 (H)) available from CitizenElectronics Co., Ltd. The monochromatic light source 11 _(g) foremitting green light was a light emitting diode E1S07-AG1A7-02(wavelength 530 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd. The monochromatic light source 11 _(b) foremitting blue light was a light emitting diode E1S07-AB1A7-02(wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H)) available fromTOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (−6.24 mm, 0) or at the position (0, −6.24 mm) and themonochromatic light source 11 _(g) for emitting green light at theposition (+5.09 mm, 0). The aperture diameter of each of the pinholes 12_(r), 12 _(g), and 12 _(b) was 150 μm. The incidence angle of the redillumination light component to the spatial light modulator 30 was setat +2.98°, and the incidence angle of the green illumination lightcomponent to the spatial light modulator 30 at −2.43°. The size of theaperture 51 of the mask 50 was 2.2 mm (W)×1.1 mm (H). The drivefrequency of the spatial light modulator 30 was 90 Hz, the hologramsassociated with the respective colors (wavelengths) were sequentiallypresented on the spatial light modulator 30, and the three monochromaticlight sources 11 _(r), 11 _(g), and 11 _(b) were sequentially activatedin synchronism therewith, whereby a full-color 3D image was clearlyobserved through the aperture 51 of the mask 50.

Sixth Embodiment

Next, the sixth embodiment of the 3D image display apparatus and 3Dimage display method according to the present invention will bedescribed. FIG. 36 is an illustration showing a configuration of the 3Dimage display apparatus 6 according to the sixth embodiment. The 3Dimage display apparatus 6 shown in this figure has an illumination lightsource section 10, a half mirror 25, a lens 20, a reflection typespatial light modulator 30, and a mask 50. The illumination light sourcesection 10, half mirror 25, and lens 20 constitute an illuminationoptical system for converting each of illumination light components ofthree wavelengths into a parallel plane wave and making the parallelplane waves incident from mutually different incident directions to thespatial light modulator 30. The lens 20 and the half mirror 25constitute a reproduced image transforming optical system for subjectingeach of reproduced light components of the three wavelengths generatedfrom holograms presented on the spatial light modulator 30, to wavefronttransformation into a virtual image or a real image. The illuminationoptical system and the reproduced image transforming optical systemshare the lens 20 and the half mirror 25.

When compared with the fourth embodiment, the 3D image display apparatus6 and 3D image display method according to the sixth embodiment aresimilar thereto in each of the illumination light source section 10,spatial light modulator 30, and mask 50, but are different therefrom inmutual arrangement of the components because of the spatial lightmodulator 30 being the reflection type spatial light modulator. Whencompared with the case of the fourth embodiment, the operation of the 3Dimage display apparatus 6, and the 3D image display method according tothe sixth embodiment are different therefrom in that the lens 20 alsoacts as the lens 40, in that each illumination light component, afterpassing through the half mirror 25, is converted into a parallel planewave by the lens 20 to enter the spatial light modulator 30, in that thereproduced light components emerge on the same side as the side wherethe illumination light components are incident to the spatial lightmodulator 30, and in that each reproduced light component is subjectedto the wavefront transformation as reflected by the half mirror 25 afterpassing through the lens 20. For the rest, the operation of the 3D imagedisplay apparatus 6, and the 3D image display method according to thesixth embodiment are theoretically almost similar to those in the fourthembodiment.

Next, a specific example of the sixth embodiment will be described. Thespatial light modulator 30 used herein was a reflection type liquidcrystal panel MD800G6 for micro monitor (pixel pitch P=12.55 μm)available from Micro Display Corp. The lens 20 also acting as the lens40 was an achromatic lens having the focal length of 60 mm. Themonochromatic light source 11 _(r) for emitting red light was a lightemitting diode CL-280SR-C (wavelength 650 nm; dimensions 1.0 (L)×0.5(W)×0.6 (H)) available from Citizen Electronics Co., Ltd. Themonochromatic light source 11 _(g) for emitting green light was a lightemitting diode E1S07-AG1A7-02 (wavelength 530 nm; dimensions 1.6 (L)×0.6(W)×1.15 (H)) available from TOYODA GOSEI Co., Ltd. The monochromaticlight source 11 _(b) for emitting blue light was a light emitting diodeE1S07-AB1A7-02 (wavelength 470 nm; dimensions 1.6 (L)×0.6 (W)×1.15 (H))available from TOYODA GOSEI Co., Ltd.

The monochromatic light source 11 _(r) for emitting red light was placedat the position (−3.02 mm, 0) or at the position (0, −3.02 mm) and themonochromatic light source 11 _(g) for emitting green light at theposition (+2.54 mm, 0). The aperture diameter of each of the pinholes 12_(r), 12 _(g), and 12 _(b) was 150 μm. The incidence angle of the redillumination light component to the spatial light modulator 30 was setat +2.98°, and the incidence angle of the green illumination lightcomponent to the spatial light modulator 30 at −2.43°. The size of theaperture 51 of the mask 50 was 2.2 mm (W)×1.1 mm (H). The drivefrequency of the spatial light modulator 30 was 90 Hz, the hologramsassociated with the respective colors (wavelengths) were sequentiallypresented on the spatial light modulator 30, and the three monochromaticlight sources 11 _(r), 11 _(g), and 11 _(b) were sequentially activatedin synchronism therewith, whereby a full-color 3D image was clearlyobserved through the aperture 51 of the mask 50.

It is apparent that the present invention can be modified in variousways, from the above description of the present invention. It is notedthat such modifications are not to be considered as departing from thespirit and scope of the present invention but all improvements obviousto those skilled in the art are to be included in the scope of claimswhich will follow.

INDUSTRIAL APPLICABILITY

According to the present invention, the spatial light modulator havingthe discrete pixel structure presents the holograms associated with therespective wavelengths. The illumination optical system converts each ofthe illumination light components of the respective wavelengths into aparallel plane wave and makes the parallel plane waves incident from themutually different incident directions to the spatial light modulator.The reproduced image transforming optical system subjects each of thereproduced images of the wavelengths generated from the hologramspresented on the spatial light modulator, to wavefront transformationinto a virtual image or a real image. The mask with the aperture isprovided on the focal plane of the optical system. Then the illuminationoptical system sets the incident directions of the respectiveillumination light components of the wavelengths to the spatial lightmodulator so that the diffracted waves of any order of the respectivereproduced light components of the wavelengths are superimposed on eachother in the aperture by the reproduced image transforming opticalsystem. This configuration permits provision of the compact andinexpensive 3D image display apparatus and others capable of providingthe color display of the clear 3D image even with use of the spatiallight modulator of a low resolution.

1. A 3D image display apparatus for making illumination light componentsof multiple wavelengths incident to a hologram, thereby generatingreproduced light components of the wavelengths from the hologram, anddisplaying a 3D image based on these reproduced light components, saidapparatus comprising: a spatial light modulator having a discrete pixelstructure for presenting holograms associated with the respectivewavelengths; an illumination optical system for converting each of theillumination light components of the wavelengths into a parallel planewave and making the parallel plane waves incident from mutuallydifferent incident directions to said spatial light modulator; areproduced image transforming optical system for subjecting each ofreproduced images of the wavelengths generated from the hologramspresented on said spatial light modulator, to wavefront transformationinto a virtual image or a real image; and a mask with an apertureprovided on a focal plane of said reproduced image transforming opticalsystem, wherein said illumination optical system sets the incidentdirections of the respective illumination light components of thewavelengths to said spatial light modulator so that diffracted waves ofany order of the respective reproduced light components of thewavelengths are superimposed on each other in said aperture after thewavefront transformation by said reproduced image transforming opticalsystem.
 2. A 3D image display apparatus according to claim 1, whereinsaid illumination optical system comprises a plurality of monochromaticlight sources having their respective output wavelengths different fromeach other; a plurality of pinholes disposed in proximity to saidrespective monochromatic light sources; and a collimating optical systemfor collimating light having been emitted from each of saidmonochromatic light sources and having passed through said pinholes. 3.A 3D image display apparatus according to claim 1, wherein saidillumination optical system comprises an achromatic lens having anidentical focal length for the light components of the wavelengths.
 4. A3D image display apparatus according to claim 1, wherein said reproducedimage transforming optical system comprises an achromatic lens having anidentical focal length for the light components of the wavelengths.
 5. A3D image display apparatus according to claim 1, wherein saidillumination optical system sets the incident directions of therespective illumination light components of the wavelengths to saidspatial light modulator so that zero-order diffracted waves of therespective reproduced light components of the wavelengths aresuperimposed on each other in said aperture after the wavefronttransformation by said reproduced image transforming optical system. 6.A 3D image display apparatus according to claim 1, wherein saidillumination optical system sets the incident directions of therespective illumination light components of the wavelengths to saidspatial light modulator so that the illumination light component of anyone specific wavelength out of the wavelengths is normally incident tosaid spatial light modulator and so that a zero-order diffracted wave ofthe reproduced light component of the specific wavelength and ahigher-order diffracted wave of the reproduced light component ofanother wavelength are superimposed on each other in said aperture afterthe wavefront transformation by said reproduced image transformingoptical system.
 7. A 3D image display apparatus according to claim 6,wherein, where P represents a pixel pitch of said spatial lightmodulator, f a focal length of said reproduced image transformingoptical system, n₁ an order of a diffracted wave of the reproduced lightcomponent of the shortest wavelength λ₁ out of the wavelengths, andn_(i) an order of a diffracted wave of a reproduced light component ofanother wavelength λ₁, an incidence angle θ_(i) of the illuminationlight component of the wavelength λ_(i) to said spatial light modulatoris expressed by the following equation:θ_(i)=sin⁻¹{(n ₁λ1 −n _(i)λ_(i))/P}, and wherein said aperture is of arectangular shape having a length of not more than λ₁f/P on each side.8. A 3D image display apparatus according to claim 1, wherein saidspatial light modulator has a transmission type structure for emittingeach of the reproduced light components on the side opposite to the sidewhere the illumination light components are incident.
 9. A 3D imagedisplay apparatus according to claim 1, wherein said spatial lightmodulator has a reflection type structure for emitting the reproducedlight components on the same side as the side where the illuminationlight components are incident, and wherein said illumination opticalsystem and said reproduced image transforming optical system share oneor more optical components.
 10. A 3D image display apparatus accordingto claim 1, wherein said spatial light modulator has microlenses mountedfor respective pixels.
 11. A 3D image display method of makingillumination light components of multiple wavelengths incident to ahologram, thereby generating reproduced light components of thewavelengths from the hologram, and displaying a 3D image based on thesereproduced light components, said method comprising the steps of:preparing a spatial light modulator having a discrete pixel structurefor presenting holograms associated with the respective wavelengths;letting an illumination optical system convert each of the illuminationlight components of the wavelengths into a parallel plane wave andletting said illumination optical system make the parallel plane wavesincident from mutually different incident directions to said spatiallight modulator; letting a reproduced image transforming optical systemsubject each of reproduced images of the wavelengths generated from theholograms presented on said spatial light modulator, to wavefronttransformation into a virtual image or a real image; placing a mask withan aperture on a focal plane of said reproduced image transformingoptical system; and letting said illumination optical system set theincident directions of the respective illumination light components ofthe wavelengths to said spatial light modulator so that diffracted wavesof any order of the respective reproduced light components of thewavelengths are superimposed on each other in said aperture after thewavefront transformation by said reproduced image transforming opticalsystem.
 12. A 3D image display method according to claim 11, whereinsaid illumination optical system comprises a plurality of monochromaticlight sources having their respective output wavelengths different fromeach other; a plurality of pinholes disposed in proximity to saidrespective monochromatic light sources; and a collimating optical systemfor collimating light having been emitted from each of saidmonochromatic light sources and having passed through said pinholes. 13.A 3D image display method according to claim 11, wherein saidillumination optical system comprises an achromatic lens having anidentical focal length for the light components of the wavelengths. 14.A 3D image display method according to claim 11, wherein said reproducedimage transforming optical system comprises an achromatic lens having anidentical focal length for the light components of the wavelengths. 15.A 3D image display method according to claim 11, wherein saidillumination optical system sets the incident directions of therespective illumination light components of the wavelengths to saidspatial light modulator so that zero-order diffracted waves of therespective reproduced light components of the wavelengths aresuperimposed on each other in said aperture after the wavefronttransformation by said reproduced image transforming optical system. 16.A 3D image display method according to claim 11, wherein saidillumination optical system sets the incident directions of therespective illumination light components of the wavelengths incident tosaid spatial light modulator so that the illumination light component ofany one specific wavelength out of the wavelengths is normally incidentto said spatial light modulator and so that a zero-order diffracted waveof the reproduced light component of the specific wavelength and ahigher-order diffracted wave of the reproduced light component ofanother wavelength are superimposed on each other in said aperture afterthe wavefront transformation by said reproduced image transformingoptical system.
 17. A 3D image display method according to claim 16,wherein, where P represents a pixel pitch of said spatial lightmodulator, f a focal length of said reproduced image transformingoptical system, n₁ an order of a diffracted wave of the reproduced lightcomponent of the shortest wavelength λ₁ out of the wavelengths, andn_(i) an order of a diffracted wave of a reproduced light component ofanother wavelength λ_(i), an incidence angle θ_(i) of the illuminationlight component of the wavelength λ_(i) to said spatial light modulatoris expressed by the following equation:θ_(i)=sin⁻¹{(n ₁λ₁ −n _(i)λ_(i))/P}, and wherein said aperture is of arectangular shape having a length of not more than λ₁f/P on each side.18. A 3D image display method according to claim 11, wherein saidspatial light modulator has a transmission type structure for emittingeach of the reproduced light components on the side opposite to the sidewhere the illumination light components are incident.
 19. A 3D imagedisplay method according to claim 11, wherein said spatial lightmodulator has a reflection type structure for emitting the reproducedlight components on the same side as the side where the illuminationlight components are incident, and wherein said illumination opticalsystem and said reproduced image transforming optical system share oneor more optical components.
 20. A 3D image display method according toclaim 11, wherein said spatial light modulator has microlenses mountedfor respective pixels.